The esters of Thiolcarbamic acids are useful for a variety of purposes. Some are active herbicides, others are effective for inhibiting the growth of micro-organisms such as bacteria, and still others are active insecticides. The following is a group of processes representative of those known in the art for the preparation of these compounds.
The process of U.S. Pat. No. 2,983,747 employs zinc chloride as a catalyst in the direct reaction of carbamyl chlorides with mercaptans to produce various thiocarbamic esters. Although the reaction can be conducted without the use of a solvent, a solvent inert to the catalyst, such as an organic solvent, must be used if a solvent is employed.
U.S. Pat. No. 2,913,327 teaches a process involving the preparation of the sodium salt of a mercaptan followed by reaction with a carbamyl chloride in the presence of a solvent. The use of the sodium salt of the mercaptan causes problems of filtration and solids handling. The use of a solvent reduces reactor capacity throughout and can create a recovery problem. Furthermore, the hydrogen evolved during the preparation of the sodium salt causes a disposal problem.
U.S. Pat. No. 3,836,524 describes a process involving the reaction of a carbamyl chloride with a mercaptan in the presence of an aqueous solution of a caustic agent. This process requires considerable agitation in order to form a high interfacial area between the two liquid phases, as well as a high caustic concentration in order to achieve the desired conversion and product purity.
U.S. Pat. No. 3,133,947 describes a process which comprises reacting a secondary or primary amine with carbonyl sulfide in the presence of a basic material which may be any amine, including a tertiary amine, and thereafter reacting the intermediate with an organic sulfate, such as a dialkyl sulfate, or a diallyl sulfate. Alkyl sulfate values are lost in this process, thus adding to the overall expense.
U.S. Pat. No. 3,151,119 describes a process involving reacting an amine with carbon monoxide and sulfur, followed by alkylation with an alkylating agent at temperatures below 20.degree. C.
Carbonyl sulfide is reacted with a primary or secondary amine in aqueous alkaline solution at temperatures of 20.degree. C or below in the process taught by U.S. Pat. No. 3,167,571. Condensation of the amine salt of the thiocarbamic acid is then effected by reaction of the salt with an organic halide.
In the process described in U.S. Pat. No. 3,954,729, a secondary amine is reacted with carbonyl sulfide in the presence of an aromatic solvent to form an amine salt of a thiocarbamic acid, which is then reacted with an alkyl halide to form the thiocarbamic acid ester.
It has been discovered that a novel process can be used for the preparation of thiolcarbamates. The object of this invention is to provide such a process, as will be more fully explained hereinbelow.